1. Field of the Invention
The present invention relates to an apparatus for controlling the driving force of a vehicle.
2. Description of Related Art
A vehicle generally employs a differential mechanism to transfer driving force from an engine to left and right drive wheels and smoothly turn a corner. In the case of a four-wheel-drive vehicle, a center differential mechanism is frequently employed. If one of the drive wheels spins without traction, the differential mechanism transmits torque from the engine to the spinning drive wheel. If this happens, the vehicle will be unable to escape from this state.
To prevent this, the differential mechanism is usually provided with a differential limiting mechanism. If one of the drive wheels loses traction, the differential limiting mechanism limits differential rotation of the differential mechanism, to help the vehicle smoothly escape from such a state.
Japanese Unexamined Patent Application Publication No. 10-217932 discloses an apparatus for controlling driving force of a vehicle. This apparatus utilizes a brake of each drive wheel, to decrease torque on the drive wheel if the drive wheel is spinning without traction, thereby escaping from the one wheel spinning state. Without employing the differential limiting mechanism, this apparatus can limit the operation of a differential mechanism.
This apparatus employs a speed sensor for each of first and second drive wheels including first and second drive wheels. If the apparatus detects from the speed sensors that a limit driving force on the first drive wheel is smaller than that on the second drive wheel, the apparatus brakes the first drive wheel, thereby increasing an apparent driving force on the first drive wheel and increasing an actual driving force on the second drive wheel. Without employing the differential limiting mechanism, this apparatus can help the vehicle come out of the drive wheel spinning state.
This apparatus, however, uses the brake against torque from the engine. Accordingly, the torque is consumed as thermal energy, to reduce driving force and wear the brake. This apparatus, therefore, is impractical.